Hydraulically amplified self-healing electrostatic actuators

ABSTRACT

Hydraulically-amplified, self-healing, electrostatic actuators that harness electrostatic and hydraulic forces to achieve various actuation modes. Electrostatic forces between electrode pairs of the actuators generated upon application of a voltage to the electrode pairs draws the electrodes in each pair towards each other to displace a liquid dielectric contained within an enclosed internal cavity of the actuators to drive actuation in various manners. The electrodes and the liquid dielectric form a self-healing capacitor whereby the liquid dielectric automatically fills breaches in the liquid dielectric resulting from dielectric breakdown.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a national phase application filing under 35U.S.C. § 371 of PCT/US18/23797 entitled “HYDRAULICALLY AMPLIFIEDSELF-HEALING ELECTROSTATIC TRANSDUCERS” filed Mar. 22, 2018, whichclaims benefit of priority to U.S. Provisional App. No. 62/613,322entitled “HYDRAULICALLY AMPLIFIED SELF-HEALING ELECTROSTATIC ACTUATORSWITH MUSCLE-LIKE PERFORMANCE” filed Jan. 3, 2018 and U.S. ProvisionalApp. No. 62/474,814 entitled “HYDRAULICALLY AMPLIFIED SELF-HEALINGELECTROSTATIC (HASEL) TRANSDUCERS” filed Mar. 22, 2017, each of theforegoing being incorporated by reference for all each disclosureteaches and discloses.

BACKGROUND 1. Field of the Invention

The present invention is directed to soft actuators and, moreparticularly, to muscle-mimetic actuators for use in robotics and thelike.

2. Relevant Background

Historically, human-made machines have tended to rely on rigidcomponents (e.g., such as metals) and typically have finite degrees offreedom. In contrast, nature makes extensive use of soft materials(e.g., mammalian muscle, cephalopods, muscular hydrostats, etc.) thatare capable of large deformation and can easily conform to theirenvironment. Soft robotics is a rapidly growing field with manypotential applications including collaborative robots that safelyinteract with humans, transducers for biomedical applications, and softgrippers capable of handling delicate and irregular objects. Actuatorsand sensors that closely mimic properties of natural muscles are keycomponents that will enable the next generation of soft robotic devices.

Existing artificial muscle transducers include pneumatic actuators,electroactive polymers (EAPs), shape memory polymers, and otherthermally-activated systems, and each has various limitations.Currently, soft robots predominantly rely on pneumatic or fluidicactuators, which limit speed and efficiency. Such actuators areversatile and prevalent, but they have specific challenges. For example,because they are connected to storage systems of pressurized fluids orpumps via channels and valves, they tend to experience fluid drag, whichcan limit bandwidth and efficiency. Further pneumatic actuators canexperience significant trade-offs between actuation speed andportability, with the response speed of untethered devices being low,and such actuators can often rely on additional sensors to controlparameters of actuation.

Dielectric elastomer actuators (DEAs), a specific type of EAP, exhibitperformance metrics that resemble biological muscle. DEAs arehyperelastic capacitors that consist of elastomeric layers sandwichedbetween compliant electrodes. When voltage is applied across the twoelectrodes, Maxwell stress causes the dielectric to reduce in thicknessand expand in area. Continuous measurement of electrical impedance ofthe hyperelastic capacitors provides information on the state ofactuation, giving DEAs self-sensing capabilities.

However, such electrically powered muscle-like actuators tend to havetheir own challenges. Being driven by high electric fields, DEAs can beprone to failure by dielectric breakdown and electrical ageing. DEAs canalso be difficult to scale up to deliver high forces, as suchapplications typically rely on large areas of dielectric (e.g., in stackactuators), which tend to be much more likely to experience prematureelectrical failure, following the Weibull distribution for dielectricbreakdown. Previous work has attempted to mitigate damage fromdielectric breakdown, but these approaches have tended to present theirown challenges. In one such approach, self-clearing electrodes have beenused to isolate dielectric breakdown sites, but the dielectric itselfremains damaged, which degrades the performance of the device. Anothersuch approach utilizes a dielectric layer consisting of a siliconesponge that is swelled with silicone oil, and the oil locallyredistributes after failure from electrical or mechanical damage; butthis approach tends only to be useful at low actuation strain.

SUMMARY

In view of at least the foregoing, embodiments described herein includea novel class of soft actuators (e.g., for soft robotics applicationsand the like), and methods for use and manufacturing of such softactuators. The novel soft actuators are referred to herein asHydraulically Amplified Self-Healing Electrostatic (HASEL) transducers(or actuators), and such HASEL transducers can provide high-performance,reliable, self-sensing, muscle-mimetic actuators that can overcomeimportant limitations of current soft actuators. HASEL actuators use anelectro-hydraulic mechanism to combine the advantages of fluidic andelectrostatic actuators. Use of liquid dielectrics can allow forharnessing hydraulic principles to scale actuation force and strain. Awide range of different modes of actuation can be achieved bypressurizing and displacing a hydraulic fluid inside of deformablestructures. HASEL actuators can be designed to linearly elongate orcontract upon application of voltage, and can feature three-dimensionalmobility. Mechanical and electrical properties can be tunedindependently. Additionally, HASEL actuators can be fabricated from avariety of materials and can be compatible with a large number offabrication techniques.

In one aspect, an electro-hydraulic actuator disclosed herein includes adeformable shell that defines an enclosed internal cavity; a liquiddielectric contained within the enclosed internal cavity; a firstelectrode disposed over a first side of the enclosed internal cavity;and a second electrode disposed over a second side of the enclosedinternal cavity, where electrostatic forces between the first and secondelectrodes upon application of a voltage to the first and secondelectrodes draws the first and second electrodes towards each other todisplace the liquid dielectric within the enclosed internal cavity.

In another aspect, a method of using an electro-hydraulic actuatorincludes applying a voltage to first and second electrodes of theactuator to generate electrostatic forces between the first and secondelectrodes; drawing the first and second electrodes towards each otherusing the electrostatic forces; displacing, during the drawing, a liquiddielectric contained within a flexible shell and disposed between thefirst and second electrodes; and flexing a portion of the flexible shellwith the displaced liquid dielectric.

In another aspect, a method of fabricating an electro-hydraulic actuatorincludes disposing a first electrode onto a first surface of a firstelastomeric shell; applying a first encapsulating layer over the firstelectrode and the first surface of the first elastomeric shell to createa first elastomeric unit; disposing a second electrode onto a firstsurface of a second elastomeric shell; applying a second encapsulatinglayer over the second electrode and the first surface of the secondelastomeric shell to create a second elastomeric unit; securing thefirst and second elastomeric units together with the first surfaces ofthe first and second elastomeric shells facing each other; and fillingan internal cavity between the first and second electrodes with a liquiddielectric.

In another aspect, a method of fabricating an electro-hydraulic actuatorincludes creating a first plurality of spaced electrodes on a firstsurface of a first film; creating a second plurality of spacedelectrodes on a first surface of a second film; placing the first filmover the second film such that the first plurality of spaced electrodesare aligned over the second plurality of spaced electrodes; sealing thefirst film to the second film at each of a plurality of spaced sealinglocations to create a plurality of pouches, wherein each pouch isdefined by: one of the first plurality of spaced electrodes, one of thesecond plurality of spaced electrodes, a portion of the first surface ofthe first film disposed between the one of the first plurality of spacedelectrodes and an adjacent of the first plurality of spaced electrodes,and a portion of the first surface of the second film disposed betweenthe one of the second plurality of spaced electrodes and an adjacent ofthe second plurality of spaced electrodes; filling each of the poucheswith a liquid dielectric via respective filling ports; and sealing eachof the filling ports.

In another aspect, a method of fabricating an electro-hydraulic actuatorincludes creating a plurality of connected, flexible pouches; fillingeach of the pouches with a liquid dielectric; positioning a respectivefirst electrode on a first side of each of the pouches, wherein adjacentones of the first electrodes are electrically connected; and positioninga respective second electrode on an opposite second side of each of thepouches, where adjacent ones of the second electrodes are electricallyconnected, and wherein the liquid dielectric in each pouch is disposedbetween its respective first and second electrode.

In another aspect, a method of fabricating an electro-hydraulic actuatorincludes bonding a first surface of a first elastomeric sheet to a firstsurface of a second elastomeric sheet; injecting a gas into an internalcavity between the first surfaces of the first and second elastomericsheets; curing the first and second elastomeric sheets together with theinjected gas disposed between the first surfaces of the first and secondelastomeric sheets; removing the gas from the internal cavity; fillingthe internal cavity with a liquid dielectric; securing a first electrodeover a second surface of the first elastomeric sheet; and securing asecond electrode over a second surface of the second elastomeric sheet.

In addition to the exemplary aspects and embodiments described above,further aspects and embodiments will become apparent by reference to thedrawings and by study of the following descriptions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C present a simplified schematic illustration of a portion ofa HASEL actuator to illustrate the self-healing nature of thetransducer.

FIGS. 2A-2E illustrate a “donut” HASEL actuator, according to oneembodiment.

FIG. 3 graphically illustrates a pull-in transition of the electrodes ofa HASEL actuator upon an increase in electrostatic force starting toexceed an increase in mechanical restoring force, causing the electrodesto abruptly pull together.

FIGS. 4A-4B illustrate non-deformed and deformed views of the HASELactuator of FIGS. 1A-1C.

FIG. 5A graphically illustrates the self-healing nature of thedonut-type HASEL actuator of FIGS. 2A-2B.

FIG. 5B graphically illustrates the self-healing nature of a“planar”-type HASEL actuator.

FIGS. 6A-6B present additional graphical illustrations of the pull-ininstabilities of the donut actuator of FIGS. 2A-2E.

FIG. 7A presents a simplified schematic illustration comparing a knowncircular DEA and a circular HASEL actuator according to an embodiment.

FIG. 7B presents plan views of the DEA and HASEL actuators of FIG. 7A toillustrate different area strains at different applied voltages.

FIG. 7C graphically illustrates the differences in area strain betweenthe DEA and HASEL actuators of FIG. 7A at different applied voltages.

FIGS. 8A-8C schematically illustrate a stack of the donut-type actuatorsof FIGS. 2A-2E without and with an applied voltage.

FIGS. 9A-9B illustrate a stack of the donut-type actuators of FIGS.2A-2E without and with an applied voltage.

FIGS. 10A-10E illustrate two stacks of the donut-type actuatorsillustrated in FIGS. 9A-9B modified to serve as a gripping mechanism.

FIGS. 11A-11B illustrate two different shapes for donut-type actuatorsthat can exhibit different behaviors because of different electrodelayouts.

FIGS. 12A-12F illustrate an implementation of donut-type HASEL actuatorsthat provides three-dimensional mobility by selectively redistributing aliquid dielectric throughout a ring-shaped deformable shell.

FIG. 13 illustrates a process of manufacturing the donut-type actuatorsof FIGS. 2A-2E.

FIG. 14 graphically illustrates a cycle life of the donut-type actuatorsof FIGS. 2A-2E.

FIG. 15A illustrates an actuation cycle of a donut-type actuator for usein measuring electromechanical efficiency of the actuator.

FIG. 15B illustrates an experimental setup for measuring theelectromechanical efficiency of the actuator in FIG. 15A.

FIGS. 15C-15I graphically illustrate various electrical measurements forthe actuation cycle of FIG. 15A.

FIGS. 16A-16C schematically illustrate the planar-type actuators of FIG.5B without and with an applied voltage.

FIG. 17A illustrates a planar-type actuator with an applied voltage anda 500 g weight hung therefrom.

FIG. 17B illustrates a planar-type actuator without and with an appliedvoltage and 250 g of weight hung therefrom.

FIG. 17C illustrates a planar-type actuator without and with an appliedvoltage and 700 g of weight hung therefrom.

FIG. 17D graphically illustrates actuation strain of the planar-typeactuator of FIG. 17B at various applied voltage levels.

FIG. 17E illustrates a plurality of planar-type actuators without andwith an applied voltage and 4 kg of weight hung therefrom.

FIG. 18A schematically illustrates a planar-type actuator with andwithout an applied voltage and a load hung therefrom.

FIG. 18B graphically illustrate time histories for displacement,velocity, and acceleration for a two-unit planar-type actuator lifting a700 g load.

FIG. 18C presents a plot of specific power during contraction for atwo-unit planar actuator lifting a 700 g load.

FIG. 18D presents a plot of specific power during contraction for asingle-unit planar actuator lifting a 1 kg load.

FIG. 19A is an exploded perspective view of a planar-type actuator,according to one embodiment.

FIG. 19B illustrates a process of fabricating the planar-type actuatorof FIG. 19A.

FIG. 19C is an exploded perspective view of a planar-type actuator,according to another embodiment.

FIG. 19D illustrates a process of fabricating the planar-type actuatorof FIG. 19C.

FIG. 19E illustrates a process of fabricating a planar-type actuator,according to another embodiment.

FIG. 20A illustrates use of a planar-type actuator to sense a positionof an arm holding a tennis ball.

FIG. 20B illustrates use of a planar-type actuator to sense a positionof an arm holding a baseball.

FIG. 20C graphically illustrates a measured capacitance of theplanar-type actuators of FIGS. 20A-20B over time for use in measuring astrain of the actuators to ascertain arm position.

FIG. 21A illustrate a “peano” HASEL actuator at increasing voltagelevels, according to one embodiment.

FIG. 21B illustrates a peano-type actuator with and without an appliedvoltage and a load hung therefrom.

FIG. 21C illustrates a peano-type actuator with and without an appliedvoltage and a load hung therefrom.

FIG. 22A graphically illustrates actuation strain of a peano-typeactuator with different electrode types and supporting different loads.

FIG. 22B illustrates a peano-type actuator without and with an appliedvoltage and a load hung therefrom.

FIG. 22C illustrates a peano-type actuator without and with an appliedvoltage and a load hung therefrom.

FIG. 23A schematically illustrates a test setup for determiningcontraction characteristics of a peano-type actuator.

FIGS. 23B-23D graphically illustrate various electrical measurementstaken during application of a voltage to the peano-type actuator.

FIG. 23E schematically illustrates a test setup for measuring afrequency response of the peano-type actuator.

FIG. 23F presents frequency response curves for the peano-type actuatorof FIG. 23E filled with liquid dielectrics of different viscosities.

FIG. 24A schematically illustrates a test setup for determining dynamicactuation characteristics of a peano-type actuator.

FIGS. 24B-24E graphically illustrate various electrical measurementstaken during application of a voltage to the peano-type actuator.

FIG. 25A illustrates a plurality of peano-type actuators arranged inparallel to scale up force generation.

FIG. 25B illustrates a plurality of peano-type actuators arranged inparallel without and with an applied voltage and a load hung therefrom.

FIG. 25C graphically illustrates a comparison of the force-straincharacteristic of a single-unit peano-type actuator to a six-unitpeano-type actuator.

FIG. 25D illustrates a plurality of peano-type actuators arranged inparallel without and with an applied voltage and a load hung therefrom.

FIG. 26A schematically illustrates a peano-type actuator without andwith an applied voltage to generate bending actuation of the actuator.

FIG. 26B illustrates respective perspective views of the views of FIG.26A.

FIG. 27A illustrates a process of fabricating a peano-type actuators,according to one embodiment.

FIG. 27B illustrates a peano-type actuator fabricated using the processof FIG. 27A.

FIG. 28 illustrates a process of fabricating a peano-type actuators,according to another embodiment.

FIG. 29 illustrates use of a planar-type actuator to power a robotic armvia an applied voltage and simultaneously sense a position of the armvia measuring a capacitance of the actuator.

FIG. 30A illustrates two peano-type actuators being used to actuate anarm to lift a ball.

FIG. 30B is similar to FIG. 30A but after the actuators have beenoperated to lift the arm and throw the ball into the air.

FIG. 30C is similar to FIG. 30A but at increasing applied voltagelevels.

FIG. 31 is a plot of a voltage signal applied to the setup of FIGS.30A-30C over time.

FIG. 32 is a plot of contraction of a peano-type actuator over timebased on optical data and capacitance data.

FIG. 33A is a peano-type actuator suspended in a colorful box.

FIG. 33B is similar to FIG. 33A but with the box partially filled with aliquid dielectric.

FIG. 33C is similar to FIG. 33B but with the box fully filed with theliquid dielectric and without a voltage being applied.

FIG. 33D is similar to FIG. 33C but with a voltage being applied.

FIG. 34 illustrates a process of fabricating a peano-type actuators,according to another embodiment.

FIG. 35 is a plot of cumulative failure probability versus electricfield strength for peano-type actuators etched for different timeperiods.

DETAILED DESCRIPTION

Embodiments described herein include a novel class of soft actuators(e.g., for soft robotics applications), and methods for use andmanufacturing of such soft actuators. The novel soft actuators arereferred to herein as Hydraulically Amplified Self-Healing Electrostatic(HASEL) transducers (or actuators), and such HASEL transducers canprovide high-performance, reliable, self-sensing, muscle-mimeticactuators that can overcome important limitations of current softactuators. HASEL actuators use an electro-hydraulic mechanism to combinethe advantages of fluidic and electrostatic actuators. Use of liquiddielectrics can allow for harnessing hydraulic principles to scaleactuation force and strain. A wide range of different modes of actuationcan be achieved by pressurizing and displacing a hydraulic fluid insideof deformable structures. HASEL actuators can be designed to linearlyelongate or contract upon application of voltage, and can featurethree-dimensional mobility. Mechanical and electrical properties can betuned independently. Additionally, HASEL actuators can be fabricatedfrom a variety of materials and can be compatible with a large number offabrication techniques.

In some embodiments, HASEL actuators are implemented as laminatedstructures consisting of electrode layers and a combination of solid andliquid dielectric materials. The layers form self-healing capacitors,which deform when a voltage is applied. Embodiments can sensedeformation via a change in capacitance when the electrodes are deformedor displaced. In some embodiments, use of liquid dielectrics inside thesoft electroactive structures can confer self-healing capabilities toHASEL actuators, as liquid dielectrics return to an insulating stateafter electrical breakdown events. The ability of HASEL actuators tofully recover from dielectric breakdown can be important for certainapplications, such as for scaling up for use in large devices and fordelivering large forces.

Some embodiments extend the HASEL actuator concepts to provide a newtype of linearly-contracting electrostatic actuator that operatessimilar to pneumatic Peano-artificial muscles, referred to herein as aPeano-HASEL actuator. The Peano-HASEL actuator can use electrodes topump dielectric fluid into a pouch, creating a geometry change thatproduces linear contraction on the application of voltage. Peano-HASELactuators can demonstrate the advantages of other HASEL actuators, whilealso being able to contract on activation. Some embodiments arecompatible with common industrial production methods, which can permitquick adoption for various applications.

FIGS. 1A-1C show an illustrative layered structure 104 of a HASELtransducer 100 and the self-healing abilities conferred to the HASELtransducer 100 from the structure 104. As illustrated, the structure 104includes a flexible shell 108 (e.g., stretchable or elastic,non-stretchable and inelastic but bendable) filled with a liquiddielectric 112 (e.g., oil). First and second stretchable, flexible, orrigid opposing electrodes 116, 117 can be placed on opposite sides ofthe shell 108. The first and second opposing electrodes 116, 117 may beany appropriate ionic or electronic conductors. The first and secondopposing electrodes 116, 117 can be separated by the shell 108 and theliquid dielectric 112. The layered structure 104 forms a capacitor thatis operable to store charge upon application of a voltage to thestructure 104. In some arrangements, the shell 108 can serve as a soliddielectric of the capacitor. In any case, upon occurrence of adielectric breakdown, the liquid dielectric 112 can refill a breach 120caused by the discharge path, thus restoring insulating properties ofthe liquid dielectric 112. This property can allow the HASEL actuator100 to self-heal from electrical damage, thereby increasing reliabilityand operational lifetime of the actuator 100.

Turning to FIGS. 2A-2E, a specific type of HASEL actuator 100 in theform of a donut-type HASEL actuator 200 is shown to illustrateconversion of electrical actuation to mechanical deformation. Thedonut-type actuator 200 includes a flexible shell or pouch 208 (e.g.,elastically deformable) that defines an enclosed internal cavity 209, aliquid dielectric 212 contained within the enclosed internal cavity 209,a first electrode 216 disposed over a first side (not labeled) of theenclosed internal cavity 209, and a second electrode 217 disposed overan opposite second side (not labeled) of the enclosed internal cavity209. For instance, the first and second electrodes 216, 217 may includerespective first and second electrical leads 221, 223 to which a voltage(e.g., DC voltage) is configured to be applied. While the first andsecond electrodes 216, 217 are illustrated as being disposed on or overan outer surface (not labeled) of the shell 208 (e.g., the firstelectrode 216 being disposed over an upper or a first outer surface andthe second electrode 217 being disposed over a lower or a second outersurface), other embodiments envision that the first and secondelectrodes 216, 217 could be disposed on or over an inner surface (notlabeled) of the shell 208 (e.g., such that the first and secondelectrodes 216, 217 are in direct contact with the liquid dielectric212). In a further embodiment, one of the first and second electrodes216, 217 may be disposed over an inner surface of the shell 208 (e.g.,on the inside of the internal cavity 209) and the other of the first andsecond electrodes 216, 217 may be disposed over an outer surface of theshell 208 (e.g., outside of the internal cavity 209). Regardless ofwhether the first and second electrodes 216, 217 are disposed inside oroutside of the internal cavity 209, the first electrode 216 may beconsidered disposed over a first side of the internal cavity 209 and thesecond electrode 217 may be considered disposed over a second side ofthe internal cavity 209.

A surface area of the shell 208 over which the first and secondelectrodes 216, 217 are disposed comprises an active area 224 of theshell 208 and a surface area of the shell 208 over which the first andsecond electrodes 216, 217 are not disposed comprises an inactive area228 of the deformable shell. While the active area 224 may be surroundedby the inactive area 228 as illustrated in the figures, otherembodiments envision that the inactive area 228 may be surrounded by theactive area 224. In any case, application of a voltage to or across thefirst and second electrodes 216, 217 (e.g., via the respective first andsecond electrical leads 221, 223) induces an electric field through theliquid dielectric 212 (e.g., and shell 208) to generate electrostaticforces that attract the first and second electrodes 216, 217 (where suchelectrostatic forces generally extend along a first reference axis 250).The generated electrostatic forces generate an electrostatic Maxwellstress on the active area 224 of the shell 204. Compare FIGS. 2A-2B. Theelectrostatic stress displaces the liquid dielectric 212 in the activearea 224, thus generating hydrostatic pressure that acts on the shell208 (e.g., in the inactive area 228) to urge the shell in one or moredifferent directions so as to move the shell 208, stretch the shell 208,etc.

Stated differently, applying a voltage (e.g., high-voltage signal)across the electrodes 216, 217 generates an electrostatic force thatcauses the electrodes 216, 217 to attract or otherwise draw together,where the attraction displaces the liquid dielectric 212 in between theelectrodes 216, 217 along a second reference axis 254 from the activearea 224 into the inactive area 228, thus coupling electrostatic stressto fluidic pressure. The pressurized liquid dielectric 212 can deform(e.g., flex) the shell 208 (e.g., in the inactive area 228 in thisembodiment) to perform mechanical work, such as lifting a load. Forinstance, the pressurized liquid dielectric 212 can, upon being forcedinto the inactive area 228, urge against the shell 208 to elasticallydeform the shell 208 in the inactive area 228, such as along a thirdreference axis 258 that is parallel to the first reference axis 250.Compare shape of inactive area 228 in FIGS. 2A, 2B, and 2D and also inFIGS. 2C and 2E. For instance, note how a thickness of the inactive area228 increases while a thickness of the active area 224 decreases thuscreating “out-of-plane” deformation of the structure. In onearrangement, the shell 208 may be inhibited from elastic deformationalong at least a portion of the second reference axis 254 in anyappropriate manner. For instance, note how the overall width of theactuator 200 remains constant in FIGS. 2A, 2B, and 2D.

As illustrated, the actuator 200 can take a toroidal, or any othersuitable shape. The ratio of the active area 224 to inactive area 228can be adjusted for scaling force and strain according to hydraulicprinciples. It can be seen that as the applied voltage increases from V1to V2, there is a small increase in actuation strain s. Compare FIGS. 2Aand 2B and also FIG. 3. However, when the voltage surpasses a thresholdV2 and increases to V3 for instance, the increase in electrostatic forcestarts to exceed the increase in mechanical restoring force (e.g., owingto the elasticity of the shell 208 and/or a load being applied to theshell 208), causing the first and second electrodes 216 ₁, 216 ₂ toabruptly pull together (see FIGS. 2D and 3); this is a characteristicfeature of a so-called pull-in or snap-through transition. Pull-intransitions and other nonlinear behaviors are features of soft activesystems that offer opportunities to improve actuation response orfunctionality and have been used to amplify the response of fluidic anddielectric elastomer (DE) actuators. After the pull-in transition,actuation strain further increases with voltage; this describes thepull-in instability that is shown in FIG. 3. Experimental data in FIGS.6A and 6B reflects this behavior (e.g., that actuation strain is smalluntil a sudden increase in strain occurs after a certain threshold).

FIGS. 4A-4B illustrate how implementations of the layered structure 104of HASEL actuators 100 can form a capacitor. Changes in capacitance canbe proportional to the amount of displacement or deformation, which canbe used for sensing and control. This property can allow HASEL actuators100 to self-sense their state of deformation, providing a feedbackmechanism to control the state of actuation. For example, driving andcontrol electronics can make use of circuits that add a low amplitudealternating current (AC) signal to the high-voltage, direct-currentdriving voltage, and from there, can obtain the impedance of thecircuits containing the deformable capacitors. Impedance data can thenbe readily converted to provide real-time information about strain ofactuation for further use in control of actuator kinematics.

FIGS. 5A-5B further illustrate self-healing behaviors of HASELtransducers 100 (e.g., as described in FIGS. 1A-1C). Specifically, FIG.5A shows self-healing of a portion of a donut-type actuator 200 withPAAm-LiCl hydrogel electrodes. As illustrated, a voltage ramp of 1 kV/sis applied until dielectric breakdown occurs, with a 10 second waitperiod after each breakdown event. The inset figure shows the sequenceof events during self-healing tests. FIG. 5B shows self-healing of aplanar-type HASEL actuator (similar to the actuator described below withreference to FIGS. 16A-16C). A linear voltage ramp at a rate of 0.5 kV/swas applied until dielectric breakdown occurred. After 1 minute, anotherlinear voltage ramp was applied until dielectric breakdown. This wasrepeated for 50 cycles to evaluate the self-healing performance of asix-unit planar HASEL actuator. Gas bubbles formed after dielectricbreakdown occurred (upper-left image). These bubbles have a lowerbreakdown strength, and electrical breakdown occurred in the samelocation but at lower voltages (lower-left image). After the gas bubbleswere removed, electrical breakdown occurred at a higher voltage and in adifferent location (top-right image). Electrical breakdown can alsooccur at a different location and at voltage higher than initialbreakdown voltage and without removing any gas bubbles (lower-rightimage). For the illustrated case, gas bubbles formed during electricalbreakdown may be trapped in the area between the stretchable conductors,which may result in a low breakdown voltage (˜5 kV). Removing the gasbubbles can restore the dielectric strength of the actuator. Someembodiments of the HASEL actuators may be fabricated with outer layersmade from gas permeable elastomers, so that gas may be automaticallypurged from the liquid dielectric.

FIGS. 6A-6B further illustrate hydraulic behaviors of HASEL actuators100 such as the donut-type actuators 200 described in relation to FIGS.2A-2E. For the sake of illustration, two donut-type HASEL actuators 200are shown in FIGS. 6A-6B, respectively, as fabricated with identicalelastomeric shells and volume of liquid dielectric, but with differentelectrode areas relative to the diameter of the pouch (the shells,liquid dielectric, and electrodes not labeled in the interest ofclarity). As shown, varying the electrode area in this way can tune thestrain and force of actuation. FIG. 6A shows linear strain as a functionof applied voltage under various loads for a first donut-type HASELactuator with an electrode diameter of 2.5 cm. This actuator achievesrelatively large strains, but generates relatively low force. FIG. 6Bshows linear strain as a function of applied voltage under various loadsfor a donut-type HASEL actuator with 1.5 cm diameter electrodes. Thisactuator generates relatively large forces, but achieves relatively lowstrains. In both cases, an electromechanical pull-in instability can beobserved, as indicated by a sudden jump in linear strain. This pull-ininstability can be harnessed to create unique modes of nonlinearactuation in certain implementations.

Some embodiments use a laminated structure of liquid and soliddielectrics to independently tune mechanical and electrical propertiesof HASEL actuators 100 to suit particular applications. FIGS. 7A-7Cillustrate tuning of HASEL actuator 100 properties in context of a HASELactuator 100 designed to resemble a circular DEA, so that the twoactuator implementations can be compared. The illustrated HASEL actuator100 expands biaxially under an applied voltage. Both the illustrativeDEA actuator and the illustrative HASEL actuator 100 may have the sametotal dielectric thickness (t) and comparable overall dielectricstrength. However, as illustrated in FIGS. 7A-7B, about one third of theHASEL dielectric consists of a liquid dielectric (e.g., the HASELactuator has a liquid dielectric thickness (t_liq) equal to one third ofthe overall thickness t). Because the liquid dielectric layer generallydoes not resist deformation (e.g., shear), the circular HASEL actuatoris overall much softer at a comparable dielectric strength, and thusdeforms at significantly lower voltages as compared to the circular DEAactuator. FIG. 7C shows a plot of area strain as a function of voltagefor the circular HASEL and circular DEA implementations. For example, at11 kV, the HASEL actuator 100 shows 46% area strain, while the DEAactuator shows 12% area strain. Varying the ratio oft to t_liq canachieve different amounts of stress and strain for a given voltage.

Different performance characteristics of the donut-type HASEL actuators200 can be altered by varying the arrangement of the actuators 200;arrangement of the electrodes 216; geometry, material, and/or thicknessof the shell 208; the volume of liquid dielectric 212 inside the shell208; and/or other parameters. For example, the shell 208 can be made outof elastomers or flexible plastics to achieve specific actuationresponses, and the frequency response of the actuator 200 can varydepending on the viscosity of the liquid dielectric 212, the overallsize of the actuator 200, etc. As one example, FIGS. 8A-9B show that theoverall stroke of actuation can be increased by stacking donut-typeHASEL actuators 200 to create a stack 300. Specifically, FIGS. 8A-8Cshow the relaxed state (without an applied voltage in FIG. 8A) and anactivated state (with an applied voltage in FIGS. 8B-8C) of a stack 300of five donut-type HASEL actuators 200. As shown, the active areas 224of adjacent actuators 200 in the stack 300 may overlap and the inactiveareas 228 of adjacent actuators 200 in the stack 300 may overlap. Inother embodiments, however, active and inactive areas 224, 228 ofadjacent actuators 200 in the stack 300 may overlap or partiallyoverlap.

In one arrangement, all of the first electrodes 216 may be electricallyinterconnected in parallel and all of the second actuators 217 may beelectrically interconnected in parallel. In another arrangement, all ofthe first electrodes 216 may be electrically interconnected in seriesand all of the second actuators 217 may be electrically interconnectedin series. FIGS. 9A-9B show an experimental result of the arrangement ofFIGS. 8A-8C (e.g., a stack 400 of five donut-type HASEL actuators, eachhaving an electrode diameter of 2.5 cm). In one arrangement, the stack400 achieved 37% linear strain, which is comparable to linear strainachieved by biological muscle and corresponds to an actuation stroke of7 mm (FIG. 2B). Hydraulic pressure is generated locally in eachdonut-type actuators 200, and liquid dielectrics 212 (not labeled) aredisplaced over short distances, allowing for high-speed actuation. Thestacked actuators readily showed large actuation response up to afrequency of at least 20 Hz. While not illustrated, one or more objectscould be disposed on top of the stack 300 and moved upwardly anddownwardly upon application of a voltage to the stack 300 and removal ofthe voltage from the stack 300.

FIGS. 10A-10B illustrate how two of the stacks 400 can be modified tocreate a gripping mechanism 500 (e.g., a “soft gripper”). As shown, theactuators within each of first and second stacks 400 ₁, 400 ₂ may beconstrained in any appropriate manner on one side to produce a tiltingmotion. For instance, each actuator may be constrained so that liquiddielectric may only flow into one half of the inactive area uponapplication of the voltage. When a DC voltage was applied to the firstand second stacks 400 ₁, 400 ₂, the device 500 grasped delicate objectssuch as a raspberry 500 (see FIGS. 10A-10C) and a raw egg 504 (see FIGS.10D-10E).

As another example of impacting performance of the actuators by alteringparameters, FIGS. 11A-11B illustrate two different shapes for donut-typeHASEL actuators 200 that can exhibit different behaviors because ofdifferent electrode layouts. In particular, FIG. 11A shows anillustrative donut-type HASEL actuator 200′ with an asterisk-shapedelectrode layout both without and with an applied voltage while FIG. 11Bshows an illustrative donut-type HASEL actuator 200″ with anannulus-shaped electrode layout both without and with an appliedvoltage. In FIG. 11B, it can be seen how the active area 224″ may besurrounded by one portion of the inactive area 228″ while anotherportion of the inactive area 228″ may be surrounded by the active area224″.

As another example of impacting performance of the actuators by alteringparameters, FIGS. 12A-12F illustrate an implementation of a donut-typeHASEL actuator 200′″ that can provide three-dimensional mobility. Theillustrated donut-type HASEL actuator 200′ is configured to selectivelyredistribute a liquid dielectric 212′″ throughout a ring-shapeddeformable shell 208′″, thereby conferring three-dimensional mobility tothe actuator 200′. The ring-shaped volume of liquid dielectric 212 maybe surrounded by an insulating skirt 211′″, with opposing electrodepairs (e.g., 216 ₁′″/217 ₁′″, etc.) spaced along the surface of theshell to create a plurality of active areas 224 ₁′″, 224 ₂′″, 224 ₃′″spaced by inactive areas 228 ₁′″, 228 ₂′″, 228 ₃′″. While three activeareas 224′″ and three inactive areas 228′″ are illustrated, it is to beunderstood that more or fewer such areas may be included.

By selectively activating electrode pairs, the actuator 200′″ mayredistribute liquid dielectric 212′″ to different regions of theinternal cavity 209′″ of the shell 208′″. For instance, displacing theliquid dielectric 212′″ from one side of the internal cavity 209′″ tothe other may cause the actuator 200′″ to tilt (e.g., by displacingliquid dielectric from the active areas 224 ₁′″ into the inactive areas228 and the active areas 224 ₂′″, 224 ₃′″). This tilting mechanism canbe tuned by precise activation of the electrode pairs, for example. Forexample, FIG. 12B shows a rest state for the specific implementationhaving three electrode pairs. As illustrated in FIG. 12D, charging agiven pair of electrodes (e.g., electrodes 216 ₁′″, 217 ₁′″) causeslocal compression which results in an overall tilt of the actuator 200′″from the normal axis 270′″. A high-voltage connection may be made withelectrode 216 ₁′″ and a ground connection may be made with electrode 217₁′″. In some implementations, all electrode pairs can be activated atonce, causing a change in the overall thickness of the actuator 200′″.As illustrated in FIGS. 12C, 12E, and 12F, such donut-type HASELactuators 200′″ can be stacked into a stack 600 to achieve furtherdegrees of three-dimensional mobility. For example, as illustrated bythe cross-section of the actuated stack 600 shown in FIG. 12F,electrical connections can be routed through the center of the stack600. Again, different modes of actuation can be achieved by varyingmaterial selection and geometry, and/or other properties.

FIG. 13 shows an illustrative process for fabricating donut-type HASELactuators 200, according to one embodiment. In Step 1, first and secondsheets of elastomeric material (e.g., for use in forming the shell 208)may be provided. For instance, this step may include casting 0.3 mmthick Polydimethylsiloxane (PDMS) sheets using acrylic molds. One sheetmay have a first diameter (e.g., 6 cm) and the other sheet may have alarger diameter (e.g., 8 cm). The larger sheet may act as an insulatingskirt (e.g., skirt 211′″ in FIG. 12A) to reduce dielectric breakdownthrough air. In Step 2, each sheet may be aligned concentrically with arespective ring member (e.g., acrylic ring). A bonding agent (e.g.,uncured PDMS) may be applied to the areas or portions of the sheets thatoverlap the ring members. For instance, the bonding agent may be appliedover respective first surfaces of the sheets and then the first surfacesof the sheets may be placed together into contact. The two halves maythen be clamped together, such as by clamping the ring members together.In Step 3, a gas (e.g., air) may be injected between the first andsecond sheets such as by inserting a needle of a syringe between the twohalves to inflate the shell. The clamped sheets may then be curedtogether to cure the bonding agent (e.g., such as in an oven at 75° C.for 30 minutes). In Step 4, the ring members may be removed. In onearrangement, a patch (e.g., Ecoflex patch) may be applied to the sheetsto serve as a fill port. In Step 5, the gas may be removed from theshell and the shell may then be filled with a liquid dielectric (e.g.,via inserting a needle through the patch and injecting with the liquiddielectric, such as 4 ml of the liquid dielectric, e.g., Envirotemp FR3transformer oil). In Step 6, flexible electrodes (e.g., circularflexible electrodes, such as Polyacrylamide-lithium chloride (PAM-LiCl)hydrogel on Kapton film) may be placed on either side of the shell(e.g., with the Kapton film facing outward).

In relation to FIG. 14, donut HASEL actuator 200 was actuated with 18 kVat 5 Hz using a reversing polarity waveform. Under an applied load of150 g, the actuation strain of the device does not noticeably diminishover the course of 1.08 million cycles.

FIG. 15A illustrates a representative process for measuring closed loopelectromechanical efficiency of HASEL actuators (e.g., donut-typeactuators 200). FIG. 15B illustrates a representative experimental setupfor measuring efficiency. As shown, a high-speed camera was used torecord displacement, y(t) (e.g., change in thickness of the inactivearea 228). A digital acquisition (DAQ) unit sent a control signal to theHV-amplifier and recorded voltage, V(t), and current I(t). Electricalenergy was calculated using voltage and current measurements. FIGS.15C-15I graphically represent various electrical measurements for theactuation cycle of FIG. 15A. In FIG. 15C, voltage was applied as asymmetric triangular pattern with maximum voltage of 21 kV and period of1.5 s. In FIGS. 15D-15E, a sudden increase in current and a change inthe slope of charge indicates pull-in transition of the donut HASELactuator. In FIG. 15F, total electrical energy consumed was 2.88 mJ. InFIGS. 15G-15I, time histories of mechanical variables during actuationwere recorded for the same cycle. Total mechanical work or energy outputwas 0.59 mJ. Electromechanical efficiency for the cycle was 21%.

Another category of HASEL actuators 100 is planar-type HASEL actuators700 as illustrated in FIGS. 16A-16C. As shown, a planar-type HASELactuator 700 may include an elastomeric shell 708 containing a liquiddielectric layer 712. First and second stretchable conductors 716, 717may cover most or all of the region containing the liquid dielectric712. When voltage is applied, electrostatic stress deforms thedielectric structure to achieve actuation modes including, for instance,uniaxial and biaxial deformation. As the first and second electrodes716, 717 may cover the entire area of the liquid dielectric 712, theentire actuator 700 may contract in thickness and expand in length inresponse to an applied voltage. To achieve uniaxial deformation, theactuator 700 may be pre-stretched and constrained in the width directionand a load may be applied in the length direction as shown in FIGS.16A-16B. When voltage is applied across the electrodes, the dielectricthickness (the dielectric thickness extending across the page in FIG.16C) is reduced and the actuator 700 expands linearly, moving the loaddownwards. When the voltage is turned off, the stored elastic energy ofthe deformed shell 708 causes the actuator 700 to return to its originalshape and length.

FIG. 17A illustrates quasi-static linear actuation of a six-unit planarHASEL actuator 800 (made up of six planar-type actuators 700 back toback) at 11.5 kV with a 500 g load. Lateral prestretch was fixed at 2.5and there was an initial prestretch of 1.5 in the direction of theweight. The use of six individual planar-type actuators 700 made iteasier to operate actuators in different orientations as change inhydrostatic pressure of the liquid dielectric may be small. In FIG. 17B,a single planar-type actuator 700 is driven by a sinusoidal signal withfrequency set near resonance and achieved 107% linear strain under a 250g load (actuation stress ˜32 kPa). The amplitude of the voltage was 13kV, which corresponds to an applied field of 10.1 kV/mm (based onun-deformed thickness of the actuator). The actuation frequency was 4.6Hz. In FIG. 17C, a two-unit planar HASEL actuator was driven by asinusoidal signal with frequency set near resonance and achieved 124%linear strain with a 700 g load (actuation stress ˜114 kPa). Amplitudeof the voltage was 14.5 kV, which corresponds to an applied field of15.5 kV/mm (based on un-deformed thickness of the actuator), and thefrequency. By tuning the relative thicknesses of the elastomer shell andliquid dielectric layer, different amounts of actuation stress andstrain can thus be achieved. FIG. 17D graphically illustrates actuationstrain of the planar-type actuator of FIG. 17B at various appliedvoltage levels. FIG. 17E illustrates a plurality of planar-typeactuators without and with an applied voltage and 4 kg of weight hungtherefrom.

FIG. 18A schematically illustrates an experimental setup of aplanar-type actuator 700 with and without an applied voltage and a loadhung therefrom. Gravimetric power and work were measured and theactuator 700 was driven by a sinusoidal voltage signal. Displacement wasmeasured using a high-speed camera (Model Phantom v710, VisionResearch). Velocity and acceleration were calculated from thedisplacement data. In FIG. 18B, time histories for displacement,velocity, and acceleration for a two-unit planar-type actuator lifting a700 g load are graphically illustrated. FIG. 18C presents a plot ofspecific power during contraction for a two-unit planar actuator liftinga 700 g load while FIG. 18D presents a plot of specific power duringcontraction for a single-unit planar actuator lifting a 1 kg load.

FIG. 19A illustrates an exploded view of a planar-type HASEL actuator700′ according to another embodiment, including a molded elastomer shell708′, first and second stretchable electrodes 716′, 717′, respectiveencapsulation layers 719′, 721′ (e.g., spin-coated elastomer layers) toencapsulate the electrodes 716′, 717′, and a liquid dielectric layer712′ inside of the elastomer shell. FIG. 19B shows an illustrativestep-by-step process for fabricating the planar-type actuator 700′ ofFIG. 19A. As illustrated, embodiments can mold two flat pieces ofelastomer for an elastomer shell (e.g., shell 708′), and then bondhydrogel conductors (e.g., first and second electrodes 716′, 717′) tothe surface. First and second encapsulating layers (e.g., layers 719′,721′) can be applied (e.g., spin-coated) on top of the electrodes toprotect and insulate them, and the two halves can be joined (e.g.,glued) together. The chambers of the elastomer shell can be filled withliquid dielectric (e.g., using a syringe or other suitable device).

FIG. 19C illustrates an exploded view of a planar-type HASEL actuator700″ according to another embodiment, including a molded elastomer shell708″, first and second stretchable electrodes 716″, 717″ (e.g., hydrogellayers), respective encapsulation layers 719″, 721″ (e.g., spin-coatedelastomer layers) to encapsulate the electrodes 716″, 717″, and a liquiddielectric layer 712″ inside of the elastomer shell. FIG. 19D shows anillustrative step-by-step process for fabricating the planar-typeactuator 700″ of FIG. 19C.

FIG. 19E illustrates another process of fabricating the planar-typeconductor 700″ of FIG. 19C. The process used the following specificmaterials: Ecoflex 00-30 for the elastomer shell and encapsulatinglayer, PAAm-LiCl hydrogels for the stretchable conductors, andEnvirotemp FR3 transformer oil for the liquid dielectric. In Step 1, twoflat rectangular pieces may be molded out of Ecoflex 00-30 for theelastomer shell. The elastomer surface was treated with a 10 wt %solution of benzophenone in ethanol. A mask was used to treat only thearea that will be patterned with electrodes. A solution for PAAm-LiClhydrogel was prepared. In Step 2, a thin plastic spacer was used thatwas cut out in the shape of the conductors as the mold for thehydrogels. The process continued by placing the spacer on the elastomersurface, pouring in the hydrogel solution, and placing a glass slide ontop of the plastic spacer to squeeze out excess hydrogel solution inStep 3. In Step 4, curing was performed under 365 nm UV light for onehour. In Step 5, a layer of Ecoflex 00-30 was spin-coated on top of theconductors to encapsulate them. In Step 6, two elastomer sheets withconductors were bonded together with a thin layer of uncured Ecoflex00-30. Uncured elastomer was not applied to sections of the shellintended to be filled with oil (those portions of the shell that are toform the internal cavity or pouch). In Step 7, the two sheets wereclamped between pieces of acrylic that have cut-outs for the liquiddielectric pouches not to be bonded together. A syringe was used to fillthese areas with air, preventing them from bonding together. The twohalves were cured together with the air inside the internal cavity. Airwas removed from the liquid dielectric pouches, and the pouches werefilled with Envirotemp FR3 transformer oil. The actuator was thenconnected to external electronics.

FIG. 20A illustrates use of a planar-type actuator 700 to sense aposition of an arm holding a tennis ball. Specifically, a robotic armpowered by a planar HASEL actuator 700 measured capacitance fordifferent payloads. The actuation voltage signal was set to 0 kV whilethe sensing voltage signal was set to an amplitude of 0.08 kV andfrequency of 2.5 kHz. Normalized capacitance measurements are plotted asa function of time in FIG. 20C, where normalized capacitance is theinstantaneous capacitance value divided by the capacitance of the armwithout any loading. A tennis ball (60 g) was dropped onto a holder atthe end of the arm. The plot in FIG. 20C shows the under-damped freeresponse of the arm which settles to an equilibrium capacitance value.In FIG. 20B, The tennis ball was removed and a baseball (125 g) wasplaced onto the end of the arm. At equilibrium, the normalizedcapacitance measured from the baseball was more than double the valuefor the tennis ball.

Yet another category of HASEL actuators is peano-type actuators.Peano-type actuators are capable of fast, muscle-mimetic, linearcontraction upon activation. This mode of actuation can exploit certaingeometric principles free of relying on stacks of actuators, initialpre-stretching, rigid components, or other techniques. As illustrated inFIG. 21A, the structure of a peano-type actuator 900 can include aflexible, but inextensible shell 908 segmented into discrete pouches 909that are each filled with a liquid dielectric 912. In other words, theinternal cavity may be segmented into a plurality of sub-cavities. Eachpouch 909 may not be in fluid communication with any of the otherpouches 909. First and second electrodes 916, 917 may be disposed overthe shell 908 of each pouch 909. The electrodes 916, 917 can becompliant or rigid, depending on the application. The portion of eachpouch 909 covered by the electrodes 916, 917 may be referred to as theactive area 924 while the uncovered portion (where contractile geometrychange occurs as discussed below) may be referred to as the inactivearea 928. To limit electrical arcing through the air around the deviceduring operation, a skirt or an insulating layer can be added to coverthe electrodes 916, 917.

In any case, the combination of each respective pouch 909, liquiddielectric 912, first and second electrodes 916, 917 may be referred toas a unit 904 and the peano-type actuator 900 may have any appropriatenumber of interconnected units 904 (e.g., such as units 904 ₁, 904 ₂,904 ₃). When an increasing voltage (V) is applied to the electrodes 916,917 of the interconnected units 904, electrostatic forces displace theliquid dielectric 912 causing the electrodes 916, 917 to progressivelydraw together and close; this forces fluid from the active areas 924into the inactive areas 928 which causes a transition from a flat crosssection to a more circular one and leads to a contractile force, F. SeeFIGS. 21A-21B.

When voltage is applied to the electrodes 916, 917, they attract due toelectrostatic forces. This attraction is governed by the Maxwellpressure:ρ=∈∈₀E²where E is the electric field between the electrodes, ∈₀ is thepermittivity of free space, and ∈ is the relative permittivity of thedielectric between the electrodes. As the electrodes attract, theyredistribute fluid from the active areas 924 into the inactive areas928. Because the shell 908 is inextensible (i.e., non-elastic), eachinactive area 928 is forced to transition from a flat cross-section to amore circular one as shown. This transition may result in a theoreticallinear contraction of up to 1−2/π, or approximately 36%, in the inactiveareas 928, as seen through simple geometry changes (e.g., as illustratedin FIG. 21B). When a weight is attached to one end of the actuator 900,the increase in fluid pressure is converted to mechanical work performedon the external load. FIGS. 21A-21B show the conversion to mechanicalforce, as well as the accompanying deformation of the actuator pouches909. FIG. 21C illustrates an experimental peano-type actuator 900 (withthree units 904) as lifting a 20 g weight on application of 8 kV acrossthe electrodes. This construction may use transparent hydrogels aselectrodes and fiberglass-reinforced tape for mounting connections.

FIGS. 22B and 22C illustrate peano-type actuators 900 using hydrogelelectrodes and aluminum electrodes, respectively while FIG. 22Agraphically illustrates actuation strain of a peano-type actuator withdifferent electrode types (hydrogel and aluminum) and supportingdifferent loads. Specifically, a modified square-wave voltage signalwith long rise and fall times (˜1 s) was used to ensure consistentactuation. The actuators were tested at 6, 8, and 10 kV; thiscorresponded to maximum electric fields of 140, 190, and 240 V μm⁻¹,respectively. The measured forcestrain curves are depicted in FIG. 22Aand show little to no difference between aluminum- andhydrogel-electrode performance, demonstrating versatility in materialselection and design. The highest load applied to the actuators was 10 N(1 kg), which corresponded to the blocking force for actuators activatedat 6 kV and was less than the blocking force at 8 and 10 kV. The 1-kgload resulted in a maximum cross-sectional stress of 6 MPa in theactuator. A strain of 10% was achieved at 10 kV with a 0.02-N (20 g)load. The shape of the observed forcestrain relation is characteristicof Peano-fluidic actuators (12). Furthermore, the monotonic decrease inforce with strain is also observed in skeletal muscle (20).

For most fluidic actuators, the limiting factor in mechanical responseis the time required to pump the working fluid throughout the system.Because peano-type actuators 900 locally pump the fluid in each unit 904(in each pouch 909 of each unit 904), the distance the fluid must travelis reduced which therefore reduces actuation time. In addition, viscousloss and design complexity are reduced by limiting or avoiding the needfor regulators and valves.

FIG. 23A schematically illustrates a test setup for determiningcontraction characteristics of a peano-type actuator 900. In this setup,the minimum cross section of the actuator used for testing was (40 mm by0.042 mm) corresponding to a maximum static stress of 2.9 MPa with a500-g load. FIGS. 23B-23D graphically illustrate various electricalmeasurements taken during application of a voltage to the peano-typeactuator. FIG. 23B shows how an 8-kV square wave was applied to theactuator. The resulting contraction response was measured, where t_(s)and t_(e) correspond to the time of initial contraction and equilibriumcontraction, respectively. Underdamped oscillations were observed afterinitial contraction. The small oscillations observed after 0.3 scorrespond to out-of-plane swinging of the load and are not part of thecharacteristic response. In FIG. 23C, peak strain rate duringcontraction as a function of load is shown. In FIG. 23D, peak andaverage specific power as a function of load are shown. FIG. 23Eschematically illustrates a test setup for measuring a frequencyresponse of the peano-type actuator. As shown, elastic bands wereattached to the bottom of the actuator and tensioned to provide aconstant 1-N restoring force. FIG. 23F presents frequency responsecurves for the peano-type actuator of FIG. 23E filled with liquiddielectrics of different viscosities. As shown, the actuator filled withFR3 liquid dielectric showed a nearly flat response up to 20 Hz. Thelower viscosity Drakeol 7 allowed maximum actuation at higherfrequencies.

FIG. 24A schematically illustrates a test setup for determining dynamicactuation characteristics of a peano-type actuator while FIGS. 24B-24Egraphically illustrate various electrical measurements taken duringapplication of a voltage to the peano-type actuator. Specifically, FIG.24B is a zoomed view of initial portion of the contraction curve in FIG.23B, with a 100 g hanging weight. A Savitsky-Golay filter was applied toposition (contraction) data to provide smoothing; derivatives of theSavitsky-Golay fits at each point provided velocity (FIG. 24C) andacceleration (FIG. 24D) data. In FIG. 24E, specific power wascalculated. Contraction time was treated as the time from the start ofcontraction t_(s) to equilibrium contraction t_(e), ignoring thesubsequent overshoot.

FIG. 25A demonstrates stack 1000 of peano-type actuators 900 in parallelto increase actuation force. Offsetting the units 904 of adjacentactuators 900 (e.g., so that active areas 924 overlap inactive areas 928on adjacent actuators 900 or in other words by about half of the lengthof a unit 904) vertically allows the expanding cross section of oneactuator 900 to nest within the pulled-in electrode area of adjacentactuators 900. Alternating electrode polarities ensures that adjacentelectrodes are at the same potential. FIG. 25B shows a 1.4-cm-thickstack of six actuators in its inactive and active state, respectively,to visualize the offset configuration. As expected, the stackdemonstrated an actuation force roughly six times that of an individualpeano-type actuator 900, as shown in FIG. 25C. FIG. 25D shows thisstack, which weighs 30 g, lifting 500 g over a strain of 4.6%.

FIGS. 26A-26B show a particular type of peano-type actuator 900′ fornovel and useful modes of actuation such as bending and twistingapplications. These applications may be useful such as for theconstruction of soft grippers for handling delicate and irregularobjects. These peano-type actuators 900′ incorporate regions that have agreater bending stiffness relative to other regions to achieve suchmodes of actuation. This stiffening can be achieved through higherstiffness materials, semi-rigid or rigid materials coupled with softjoints, and/or in other suitable manners. The stiffened regions can belocated along all or portions of the actuator shell to achieve variousmodes of actuation.

In FIG. 26A, the peano-type actuator 900′ achieves bending modes ofactuation by configuring a first portion 908 ₁′ of the shell (e.g., aleft or bottom side in FIG. 26A) to have a greater bending stiffnessthan a second portion 908 ₂′ of the shell (e.g. a right or upper side inFIG. 26A). Thus, the pouch 909′ of each unit 908′ is generallysurrounded by the first portion 908 ₁′ of the shell on one side and thesecond portion 908 ₂′ of the shell on the other side. When a voltage isapplied, inhomogeneous deformation of the pouches 909′ leads topreferential contraction on the right, and overall bending. FIG. 26Bshows a perspective view, illustrating the deformation during actuation.Many other approaches are possible for varying actuation. For example,some implementations include twisting or torsional actuators, whichincorporate strips of stiffened regions on either side to force atwisting motion on application of voltage. Other implementations includebidirectional bending actuators. For example, by placing two bendingPeano-HASEL actuators back-to-back with the stiffened side in themiddle, bending actuation can be achieved in either direction byapplying voltage to one actuator or the other. Other implementations canachieve bidirectional bending actuation through a three-layerconstruction: a central stiff layer with incorporated electrodes, andtwo flexible outer layers (one on either side) that can be selectivelyactivated by application of voltage.

FIG. 27A shows an illustrative process for fabricating peano-typeactuators 900. In Step 1, a first plurality of spaced electrodes arecreated on a first surface of a first film and a second plurality ofspaced electrodes are crated on a first surface of a second film. Forinstance, each film may be in the nature of a metallized, heat-sealablebiaxially-oriented polypropylene (BOPP) film. For instance, the BOPPfilms may include a layer of vacuum-deposited aluminum on one side. Anelectrode pattern can be defined on the film by using a PDMS protectivemask and submerging in a potassium hydroxide (KOH) etch. For instance,using a soft mask to preserve the electrode area, the aluminum layer maybe etched using a 1 wt % KOH solution until excess metal is removed. InStep 2, the first film may be placed over the second film such that thefirst plurality of spaced electrodes are aligned over the secondplurality of spaced electrodes, and then the first and second films maybe sealed together at each of a plurality of spaced sealing locations tocreate a plurality of pouches. Each such pouch is defined by: a) one ofthe first plurality of spaced electrodes, b) one of the second pluralityof spaced electrodes, a) a portion of the first surface of the firstfilm disposed between the one of the first plurality of spacedelectrodes and an adjacent of the first plurality of spaced electrodes,and d) a portion of the first surface of the second film disposedbetween the one of the second plurality of spaced electrodes and anadjacent of the second plurality of spaced electrodes;

For instance, the two films can be placed back-to-back and sealedtogether to form the discrete pouches using a heat press with a custommetal die. As shown, the heated brass die may seal the first and secondfilms together at each of the sealing locations. Access ports can beleft in each pouch for filling. In Step 3, each pouch can be filled withliquid dielectric (e.g., Envirotemp FR3 transformer oil via syringe orthe like) and subsequently sealed (e.g., using a heated metal bar) inStep 4. FIG. 27B shows an illustrative final constructed actuator, whichincludes a skirt along the outside to prevent electrical arcing throughair during operation. The shell materials can include: heat-sealablethermoplastics, reinforced elastomers, cast plastics, etc. A variety ofdielectric fluids can also be used. Electrodes can be implemented withcompliant materials, such as: carbon-based conductors such as conductiveelastomers, fabrics, carbon grease; thin metal layers, such asvacuum-deposited metal layers or conductive tapes; ionic conductors,such as hydrogels and ionic liquids; etc. Other implementations can userigid conductors for actuation.

FIG. 28 illustrates a process of fabricating a peano-type actuators,according to another embodiment. Section A illustrates basic componentsof a peano-type actuator 900 to be fabricated according to the processof FIG. 28. As shown in Section B, two BOPP sheets may be placed betweentwo layers of Kapton film and sealed using a heated brass-rod die. Thedie may be designed to give pouches (e.g., 2 cm by 4 cm) with accessports (e.g., 2 mm) for filling with a liquid dielectric. A PDMS sheetmay be placed below the Kapton as a load-dispersing layer. In Section C,the pouches may be filled with a liquid dielectric (FR3), such as byusing a syringe. In Section D, a heated rod may be used to seal thefilling ports. In Section E, PDMS-backed hydrogel electrodes may beplaced on each side of the pouches. Section F shows a finished actuator.

FIG. 29 illustrates use of a planar-type actuator to power a robotic armvia an applied voltage and simultaneously sense a position of the armvia measuring a capacitance of the actuator. In other words, HASELactuators can simultaneously serve as strain sensors. For instance,driving and control electronics may make use of circuits that add a lowamplitude AC signal to a high-voltage DC driving voltage, therebyenabling obtaining of the impedance of the circuits containing thehyper-elastic capacitors. Relative capacitance can be recorded as afunction of time to indicate the position of the arm. As shown, measuredcapacitance is low when the arm is fully flexed (on the left) andcapacitance is high when the arm is extended (on the right). The bottomplot shows details of the applied voltage signal (solid line) andmeasured relative capacitance (dashed line), C/C_(o), where C ismeasured capacitance and C_(o) is the minimum value for capacitance.Voltage and capacitance are ˜90° out of phase, which is typical for adriven damped oscillator. In one arrangement, a first capacitance of oneof the first and second electrodes may be measured at a first voltage(or before applying a voltage) and a second capacitance of the one ofthe first and second electrodes may be measured at a second voltage, andthe a difference between the first and second capacitances may be usedto determine a strain of the one of the first and second electrodesrelative to the other of first and second electrodes during displacementor pressurizing of the liquid dielectric.

FIG. 30A illustrates two peano-type actuators 900 in parallel fordemonstrating fast and controllable actuation. As shown in FIG. 30B, byapplying a 13-kV voltage step, these actuators contracted fast enough tothrow a ping-pong ball 24 cm into the air. Labeled times are measuredfrom the start of contraction. FIG. 30C shows how incrementing voltageallows for controllable actuation of the arm, as shown in theprogression of images with increasing voltage from left to right. Thehorizontal lines mark the position of the top of the ball forcomparison. The ruler to the left of each picture shows 1-cm incrementsfor scale. Not all details of the actuators 900 are illustrated in FIGS.30A-30C in the interest of clarity. FIG. 31 illustrates the full signalused in testing the lever arm setup of FIGS. 30A-30B. The three regionsare meant to show the versatility of actuation for peano-type actuators900. Section I demonstrates voltage steps of 1-kV increments from 0 to12 kV with 0.75 s hold time at each voltage to show the accuratepositional control with respect to input voltage. Section II is anoffset sine wave constructed by reflecting every other cycle over thex-axis. This waveform is meant to demonstrate smooth and muscle-mimeticactuation. Section III is a 13-kV voltage step to demonstrate thehigh-speed operation of the actuators.

FIG. 32 is a plot of dimensionless capacitance and optically trackedposition data for a single actuator under the influence of a varyingvoltage signal. Capacitance data is multiplied by a constant scalefactor to provide agreement with position data.

FIG. 33A is a peano-type actuator 900 suspended in a colorful box. FIG.33B is similar to FIG. 33A but with the box partially filled with aliquid dielectric. FIG. 33 C is similar to FIG. 33B but with the boxfully filed with the liquid dielectric and without a voltage beingapplied. This figure shows how the actuator 900 is nearly or fullyinvisible. FIG. 33D is similar to FIG. 33C but with the voltage beingapplied.

FIG. 34 illustrates a process of fabricating a peano-type actuators 900,according to another embodiment, and using hydrogel electrodes. In Step1, a PDMS pre-polymer layer may be spin-coated or cast onto a wafer(e.g., acrylic plate) and cured. In Step 2, the PDMS surface may betreated with a solution of benzophenone in ethanol (e.g., 10 wt %). Amask may be used to treat only the area to be patterned with electrodes.In Step 3, a solution may be prepared for PAAm-LiCl hydrogel, and a thinplastic spacer may be used that is cut out in the desired shape of theelectrodes as the mold for the hydrogels. The spacer may placed on thePDMS surface, the hydrogel solution may be poured in, and a glass slidemay be placed on top of the plastic spacer to squeeze out excesshydrogel solution. In Step 4, curing may be performed (e.g., under 365nm UV light for one hour). In Step 5, the hydrogel/PDMS structure may becut out (e.g., with a laser cutter) and set aside until needed. Theshell may then be prepared using a heat press with a metal die to definepouch regions. Each pouch may be filled with liquid dielectric throughaccess ports, and each access port may be heat stamped using a heatedmetal bar. The actuator may then be assembled by laying thehydrogel/PDMS electrode structure onto the pouch with the hydrogel sidedown and aligning them. The hydrogel may then be bonded to the surfaceusing a cyanoacrylate glue. In Step 6, excess PDMS/hydrogel may beremoved to expose completed electrodes.

FIG. 35 is a plot of cumulative failure probability versus electricfield strength for peano-type actuators etched for different timeperiods. As shown, breakdown voltages of single-layer BOPP film withthin heat-sealing copolymer layer on one side are illustrated. Onesample was etched for 4 minutes in 1.5 wt % aqueous KOH solution, whilethe other was etched for 60 minutes in the same solution. Theseconditions were meant to verify that the KOH etch did not degrade thebreakdown strength of BOPP samples. Electrodes were PAAm hydrogelsswollen with an 8 M LiCl solution. A voltage ramp of 500 V/s was applieduntil breakdown occurred, with 15 tests conducted under each condition.The data was fit to a two-parameter Weibull distribution to determinethe characteristic breakdown voltages of 650 V/μm (4 minutes) and 685V/μm (60 minutes).

Various embodiments can include various types of features and/or canaddress various design (e.g., operational) considerations. For example,pouches filled with liquid dielectrics can be segmented to controlhydraulic pressure in specific regions. Segmented pouches can alsomitigate the influence of gravity, preventing the liquid dielectric fromflowing to regions of the pouch with lowest gravitational potential.Segmentation can allow actuators to operate in a variety of positionsand orientations without loss of functionality. An example ofsegmentation is shown in FIG. 17E. By using designs that displace theliquid dielectric only over short distances, energy losses caused byfluid drag can be reduced, and maximum frequency of actuation can beincreased. Additionally, the response time can be inversely correlatedto the size of the actuator, such that scaling down the actuator canincrease the maximum frequency of actuation. In some embodiments,electromechanical pull-in or snap-through instabilities (e.g., asdescribed with reference to FIGS. 6A-6B) can give rise to actuatorsexhibiting actuation responses that are highly nonlinear anddiscontinuous (e.g., for use as “binary” actuators). In addition totheir inherent ability to self-heal from electrical damage, someembodiments of HASEL transducers further include features forself-healing from mechanical damage, such as by incorporatingmechanically self-healing ionic conductors and mechanically self-healingelastomers. Such embodiments can effectively be fully self-healing fromboth mechanical and electrical damage, which can yield highly durabledevices with long lifetimes. The embodiments described herein, as wellas modifications to those embodiments, can yield wide variety of HASELactuators that can be fabricated, and/or arranged in arrays or otherstructures, to scale up force, increase stroke, achieve modes ofactuation with higher complexity, etc.

The various techniques can be implemented with any suitable hardwareand/or software component(s) and/or module(s), including, but notlimited to circuits, application specific integrated circuits (ASICs),general purpose processors, digital signal processors (DSPs), fieldprogrammable gate arrays (FPGAs), programmable logic devices (PLD),discrete gates, transistor logic devices, discrete hardware components,or combinations thereof. For example, steps of methods or algorithms, orother functionality described in connection with embodiments, can beembodied directly in hardware, in a software module executed by aprocessor, or in a combination of the two. A software module may residein any form of tangible storage medium. Some examples of storage mediathat may be used include random access memory (RAM), read only memory(ROM), flash memory, EPROM memory, EEPROM memory, registers, a harddisk, a removable disk, a CD-ROM and so forth. A storage medium may becoupled to a processor such that the processor can read informationfrom, and write information to, the storage medium. In the alternative,the storage medium may be integral to the processor. A software modulemay be a single instruction, or many instructions, and may bedistributed over several different code segments, among differentprograms, and across multiple storage media. Thus, a computer programproduct may perform operations presented herein. For example, such acomputer program product may be a computer readable tangible mediumhaving instructions tangibly stored (and/or encoded) thereon, theinstructions being executable by one or more processors to perform theoperations described herein. The computer program product may includepackaging material. Software or instructions may also be transmittedover a transmission medium. For example, software may be transmittedfrom a website, server, or other remote source using a transmissionmedium such as a coaxial cable, fiber optic cable, twisted pair, digitalsubscriber line (DSL), or wireless technology such as infrared, radio,or microwave.

The methods disclosed herein include one or more actions for achievingthe described method. The method and/or actions can be interchanged withone another without departing from the scope of the claims. In otherwords, unless a specific order of actions is specified, the order and/oruse of specific actions can be modified without departing from the scopeof the claims. The various operations of methods and functions ofcertain system components described above can be performed by anysuitable means capable of performing the corresponding functions.

Other examples and implementations are within the scope and spirit ofthe disclosure and appended claims. For example, features implementingfunctions can also be physically located at various positions, includingbeing distributed such that portions of functions are implemented atdifferent physical locations. Also, as used herein, including in theclaims, “or” as used in a list of items prefaced by “at least one of”indicates a disjunctive list such that, for example, a list of “at leastone of A, B, or C” means A or B or C or AB or AC or BC or ABC (i.e., Aand B and C). Further, the term “exemplary” does not mean that thedescribed example is preferred or better than other examples.

Various changes, substitutions, and alterations to the techniquesdescribed herein can be made without departing from the technology ofthe teachings as defined by the appended claims. Moreover, the scope ofthe disclosure and claims is not limited to the particular aspects ofthe process, machine, manufacture, composition of matter, means,methods, and actions described above. Processes, machines, manufacture,compositions of matter, means, methods, or actions, presently existingor later to be developed, that perform substantially the same functionor achieve substantially the same result as the corresponding aspectsdescribed herein can be utilized. Accordingly, the appended claimsinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or actions.

It will be readily appreciated that many deviations may be made from thespecific embodiments disclosed in the specification without departingfrom the spirit and scope of the invention. For instance, somearrangements envision that different data item types may requiredifferent amounts of processing time by the processors and this may betaken account in the above discussion in any appropriate manner.

As mentioned, embodiments disclosed herein can be implemented as one ormore computer program products, i.e., one or more modules of computerprogram instructions encoded on a computer-readable medium for executionby, or to control the operation of, data processing apparatus(processors, cores, etc.). The computer-readable medium can be amachine-readable storage device, a machine-readable storage substrate, amemory device, a composition of matter affecting a machine-readablepropagated signal, or a combination of one or more of them. In additionto hardware, code that creates an execution environment for the computerprogram in question may be provided, e.g., code that constitutesprocessor firmware, a protocol stack, a database management system, anoperating system, or a combination of one or more of them.

Certain features that are described in this specification in the contextof separate embodiments can also be implemented in combination in asingle embodiment. Conversely, various features that are described inthe context of a single embodiment can also be implemented in multipleembodiments separately or in any suitable subcombination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a sub combination.

We claim:
 1. An electro-hydraulic actuator, comprising, a deformableshell that defines an enclosed internal cavity; a liquid dielectriccontained within the enclosed internal cavity; a first electrodedisposed over a first side of the enclosed internal cavity; and a secondelectrode disposed over a second side of the enclosed internal cavity,wherein the first and second electrodes are configured such that anelectrostatic force between the first and second electrodes uponapplication of a voltage to one of the first and second electrodes drawsthe first and second electrodes towards each other to displace theliquid dielectric within the enclosed internal cavity, are disposedcomprises an active area of the deformable shell, wherein a surface areaof the deformable shell over which the first and second electrodes arenot disposed comprises an inactive area of the deformable shell, whereinthe electrostatic force between the first and second electrodes isconfigured to displace the liquid dielectric within the enclosedinternal cavity from the active area of the shell to the inactive areaof the shell, wherein the first and second electrodes comprise a firstpair of electrodes, wherein the actuator comprises one or moreadditional pairs of electrodes that are each disposed over one or moreadditional active areas of the flexible shell, wherein each adjacentpair of the active areas is spaced by an inactive area, wherein theinternal cavity comprises a plurality of sub-cavities, wherein eachsub-cavity is surrounded by one or the active areas and one of theinactive areas, and wherein the liquid dielectric is impassable from onesub-cavity to another sub-cavity.
 2. The actuator of claim 1, whereinthe deformable shell further includes a central inactive area that issurrounded by the first pair of electrodes and the one or moreadditional pairs of electrodes.
 3. A system, comprising: a stack of aplurality of the actuators of claim 1, wherein the first actuators inthe stack are electrically connected in parallel or series, and whereinthe second actuators in the stack are electrically connected in parallelor series.
 4. The actuator of claim 1, wherein a first portion of thedeformable shell on the first side of the internal cavity comprises afirst stiffness, wherein a second portion of the deformable shell on thesecond side of the internal cavity comprises a second stiffness, andwherein the first stiffness is greater than the second stiffness.
 5. Theactuator of claim 1, wherein the first and second electrodes, thedeformable shell, and the liquid dielectric form a self-healingcapacitor, and wherein the liquid dielectric is configured forautomatically filing breaches in the liquid dielectric resulting fromdielectric breakdown.
 6. A method of using an electro-hydraulicactuator, comprising applying a voltage to one of a first and a secondelectrode of the actuator to generate an electrostatic force between thefirst and second electrodes; drawing the first and second electrodestowards each other using the electrostatic force; displacing, during thedrawing, a liquid dielectric contained within a flexible shell anddisposed between the first and second electrodes; and flexing a portionof the flexible shell with the displaced liquid dielectric, wherein asurface area of the flexible shell over which the first and secondelectrodes are disposed comprises an active area of the flexible shell,wherein a surface area of the flexible shell over which the first andsecond electrodes are not disposed comprises an inactive area of theflexible shell, and wherein the displacing includes: displacing theliquid dielectric from the active area of the shell to the inactive areaof the shell, wherein the first and second electrodes comprise a firstpair of electrodes, wherein one or more additional pairs of electrodesare disposed over additional active areas of the flexible shell andwherein each adjacent pair of the active areas is spaced by an inactivearea, and wherein the displacing includes; displacing the liquiddielectric from the active areas to the inactive areas; and drawing theelectrodes in each adjacent pair of electrodes towards each other inresponse to the liquid dielectric being displaced from the active areasto the inactive areas.
 7. The method of claim 6, wherein theelectrostatic force extends in a direction of a first reference axis,and wherein the displacing includes: displacing the liquid dielectric ina direction of a second reference axis that is perpendicular to thefirst reference axis.
 8. The method of claim 7, wherein the flexingincludes: urging the portion of the flexible shell along the secondreference axis.
 9. The method of claim 8, further including; inhibitingflexure of the flexible shell in a direction of a third reference axisthat is perpendicular to the first and second reference axes.
 10. Themethod of claim 6, wherein the flexing includes elastically flexing theportion of the flexible shell.
 11. The method of claim 6, wherein theflexing occurs free of elastically stretching the portion of theflexible shell.
 12. The method of claim 6, further including: measuringa first capacitance of one of the first and second electrodes before theapplying; measuring a second capacitance of the one of the first andsecond electrodes after the applying, and using a difference between thefirst and second capacitances to determine a strain of the one of thefirst and second electrodes relative to the other of first and secondelectrodes during the displacing.
 13. The method of claim 6, wherein thedisplacing includes; displacing the liquid dielectric from one of theactive areas of the shell to another of the active areas of the shell,wherein a voltage is not applied to the pair of electrodes of theanother active area of the shell.
 14. The method of claim 6, furtherincluding, bending the actuator in response to the drawing theelectrodes in each adjacent pair of electrodes toward each other. 15.The method of claim 14, further including: twisting the actuator inresponse to the drawing the electrodes in each adjacent pair ofelectrodes towards each other.
 16. An electro-hydraulic actuator,comprising: a deformable shell that defines an enclosed internal cavity;a liquid dielectric contained within the enclosed internal cavity; afirst electrode disposed over a first side of the enclosed internalcavity; and a second electrode disposed over a second side of theenclosed internal cavity, wherein the first and second electrodes areconfigured such that an electrostatic force between the first and secondelectrodes upon application of a voltage to one of the first and secondelectrodes draws the first and second electrodes towards each other todisplace the liquid dielectric within the enclosed internal cavity,wherein a first portion of the deformable shell on the first side of theinternal cavity comprises a first stiffness, wherein a second portion ofthe deformable shell on the second side of the internal cavity comprisesa second stiffness, and wherein the first stiffness is greater than thesecond stiffness.
 17. The actuator of claim 16, wherein a surface areaof the deformable shell over which the first and second electrodes aredisposed comprises an active area of the deformable shell, wherein asurface area of the deformable shell over which the first and secondelectrodes are not disposed comprises an inactive area of the deformableshell, and wherein the electrostatic forces between the first and secondelectrodes displaces the liquid dielectric within the enclosed internalcavity from the active area of the shell to the inactive area of theshell.
 18. The actuator of claim 17, wherein the first and secondelectrodes comprise a first pair of electrodes, wherein the actuatorcomprises one or more additional pairs of electrodes that are eachdisposed over an active area of the flexible shell, and wherein eachadjacent pair of the active areas is spaced by an inactive area.
 19. Theactuator of claim 16, wherein the first and second electrodes, thedeformable shell, and the liquid dielectric form a self-healingcapacitor, and wherein the liquid dielectric is configured toautomatically fill breaches in the liquid dielectric resulting fromdielectric breakdown.
 20. A method of using an electro-hydraulicactuator, comprising: applying a voltage to one of a first and a secondelectrode of the actuator to generate an electrostatic force between thefirst and second electrodes; drawing the first and second electrodestowards each other using the electrostatic force; displacing, during thedrawing, a liquid dielectric contained within a flexible shell anddisposed between the first and second electrodes, flexing a portion ofthe flexible shell with the displaced liquid dielectric; measuring afirst capacitance of one of the first and second electrodes before theapplying; measuring a second capacitance of the one of the first andsecond electrodes after the applying, and using a difference between thefirst and second capacitances to determine a strain of the one of thefirst and second electrodes relative to the other of first and secondelectrodes during the displacing.